Differential Expression of Capsaicin-, Menthol-, and Mustard Oil-Sensitive Receptors in Naive Rat Geniculate Ganglion Neurons

• Published in: Chemical senses 2006-09, Vol.31 (7), p.681-688
• Main Authors: Katsura, Hirokazu, Tsuzuki, Kenzo, Noguchi, Koichi, Sakagami, Masafumi
• Format: Article
• Language: English
• Subjects: Animals; Ankyrins; Biological and medical sciences; Calcium Channels - biosynthesis; Calcium Channels - drug effects; Calcium Channels - physiology; Capsaicin - pharmacology; Fundamental and applied biological sciences. Psychology; geniculate ganglion; Geniculate Ganglion - drug effects; Geniculate Ganglion - metabolism; Geniculate Ganglion - ultrastructure; Male; Menthol - pharmacology; Mustard Plant; Nerve Fibers, Myelinated - metabolism; Nerve Fibers, Unmyelinated - metabolism; Neurons - drug effects; Neurons - metabolism; NF200; Olfactory system and olfaction. Gustatory system and gustation; Plant Oils - pharmacology; Rats; Rats, Sprague-Dawley; RNA, Messenger - biosynthesis; TRPA1; TRPA1 Cation Channel; TRPC Cation Channels; TRPM Cation Channels - biosynthesis; TRPM Cation Channels - drug effects; TRPM Cation Channels - physiology; TRPM8; TRPV Cation Channels - biosynthesis; TRPV Cation Channels - drug effects; TRPV Cation Channels - physiology; TRPV1; Vertebrates: nervous system and sense organs
• ISSN: 0379-864X; 1464-3553
• DOI: 10.1093/chemse/bjl009

The roles of capsaicin, menthol, and mustard oils and their receptors in geniculate ganglion (GG) neurons still remain to be elucidated. These receptors belong to the transient receptor potential (TRP) family. Capsaicin-, menthol-, and mustard oil-sensitive receptors are TRPV1, TRPM8, and TRPA1, respectively. The present study aimed to investigate the expression of TRPV1, TRPM8, and TRPA1 in naive rat GG neurons. Furthermore, we examined whether these TRP-expressing GG neurons are myelinated A-fiber or unmyelinated C-fiber neurons. Firstly, using reverse transcription–polymerase chain reaction, TRPV1 mRNA and TRPA1 mRNA were distinctly detected in the naive GG. TRPM8 mRNA was faintly detected. Secondly, using in situ hybridization, TRPV1 mRNA– or TRPA1 mRNA–labeled neurons (signal/noise ratio ≥ 10) were observed in 15–20% of GG neurons. Few neurons were labeled by TRPM8 mRNA. Thirdly, neurofilament 200 (NF200) protein, a marker of mylinated A-fiber neurons, was detected in 57% of naive GG neurons. Coexpression of TRPV1 mRNA or TRPA1 mRNA with NF200 was detected in 10% of GG neurons. The present study confirmed the expression of the TRP receptors in the naive GG. The possible roles of TRP receptors in naive GG neurons in somatosensory or gustatory function were suggested.